I believe I saw San Francisco as the font used in iOS UI kit that comes with the software - I was very pleasantly surprised since I'm on Windows. I think this was in one of previous versions.
Now that I needed to use XD for an iOS app I noticed the font is missing. When I select any text in the UI kit the fields that show the font name and font weight are blank.
Is this just me or do others have this issue too ? I'm running the latest update of XD.
What you were seeing was the file that had the SF font as the default, but we displayed a fallback font instead. So you weren't actually seeing the SF Font. That being said, the new iOS UI Kit provided by Apple has the font in the ZIP file, so you can probably install it from there.
Hope that helps!